In a conventional device package such as the device package 100 illustrated in FIG. 1, a die 110 is placed above a substrate 120 and the die 110 is encapsulated within a mold 130. The die 110 can include solder balls 115 to electrically couple with the substrate 120. As seen, the mold 130 can fill the space between the die 110 and the substrate 120—the “in-between space”. For example, during fabrication, the material for the mold 130 may fill the in-between space through capillary action.
One disadvantage of the device package 100 is that there can be high mold stress on the die 110. For example, during the molding process, the die 110 can be subjected to high mold pressure. During operation of the device package 100, a mismatch in the coefficient of thermal expansion (CTE) among the die 110, the substrate 120 and the mold 130 can have reliability implications for the device package 100.
Another disadvantage is the relatively high ratio of the dielectric constant (Dk) to the dissipation factor (Df)—i.e., relatively high Dk/Df—of the mold 130. For example, the die 110 may be an electromagnetic compatibility (EMC) filter capable of high frequency operation. The EMC filter's performance can suffer as a result of the high Dk/Df of the mold 130.
FIG. 2 illustrates another conventional device package 200 that addresses the high Dk/Df problem. The device package 200 differs from the device package 100 in that the device package 200 includes underfill (UF) dams 240 that create an air cavity 250 in the in-between space, i.e., in the space between the die 110 and the substrate 120. The Dk/Df of air is low in comparison, and thus the performance of the die 110 can be improved.
During fabrication, the die 110 can be attached to the substrate 120, and the material for the UF dam 240 can be dispensed around the edge of the in-between space. Thereafter, the mold 130 can be formed. The UF dam 240, which is formed from an epoxy, prevents the mold 130 from flowing into the in-between space so as to maintain the air cavity 250.
One disadvantage of the device package 200 is that the UF material can bleed in all directions after being dispensed. In other words, the UF material does not remain in place during fabrication after being dispensed. As a result, the size of the air cavity 250 can be reduced. But perhaps more significant, the bleeding can result in an increase in the “keep-out” zone. For example, as seen in FIG. 2, the UF dam 240 can bleed out laterally away from the sidewalls of the die 110. To account for such bleed out, another component—e.g., passive capacitor, inductor, etc., or another die—must be placed far enough away so as to be unaffected by the bleed out. This can result in the component density being reduced.